The present invention relates to foam compositions which may be flame retardant and methods for making same wherein reaction pressures can be controlled during the foaming process. The foam may be produced with a variety of densities, tensile strength, cell structures and other physical properties.
Plastic foams have been utilized as thermal insulating materials, light weight construction materials, and flotation materials and for a wide variety of other uses because of their excellent properties. Heretofore, their use has been limited in environments where there is danger of fire because of their substantial fuel contribution, their contribution to rapid flame spread and the fact that they generate large quantities of noxious smoke on thermal decomposition when burned or heated to an elevated temperature. This has limited the commercial development of plastic foams. Large amounts of money and much research time have been expended in attempts to alleviate these problems.
With the present interest in conserving heating fuel, many existing buildings are installing additional insulation, and newly constructed buildings are including more insulation than was formerly used.
The most commonly used type of foam insulation for existing structures are urea formaldehyde foams, which are foamed in place between the outside wall and the inside wall of the structure. Unfortunately, the urea formaldehyde foam spontaneously decomposes, releasing formaldehyde fumes in quantities which may be toxic. The use of urea formaldehyde foams in construction is prohibited in some building codes for this reason.
Another type of material often used for insulation is polyurethane foam. However, polyurethane foam provides a substantial fuel contribution, spreads flame rapidly, and releases toxic gases including carbon dioxide, carbon monoxide and hydrogen cyanide when burned. The use of polyurethane foam for retrofit is not completely satisfactory because of the high reaction pressures generated during the foaming process, which can be sufficient to separate the wallboard from the wall studs.
Rigid polyurethane foams are generally prepared by reacting an organic polyisocyanate with a polyol. For most commercial purposes, the reaction is conducted in the presence of a foaming agent, surfactant, catalyst and possibly other ingredients. In order to reduce the cost of preparing these foams, efforts have been made to employ polysaccharides such as starch or cellulose as a polyol reactant in their preparation. The use of such substrates has been unsatisfactory because of the poor physical properties of the foams produced unless they have been modified in some way or supplemented with conventional industrial polyols. Oxyalkylated starch yields satisfactory foams, but the direct oxyalkylation of starch results in uncontrolled degradation or decomposition of the starch. When such products are used in the production of foams, the foams do not have uniform chemical or physical properties.
A satisfactory process for utilizing starch as a compenent in the preparation of polyurethane foams is disclosed in U.S. Pat. No. 3,277,213. In this process, starch is added to a polyhydric alcohol containing at least two hydroxyl groups in a proportion equivalent to at least 0.5 mole of the alcohol per mole of glucose unit weight of starch in the presence of an acid catalyst. The resulting mixutre is then oxyalkylated to yield a polyether polyol suitable for use in preparating polyurethane foams of excellent physical properties.
U.S. Pat. No. 3,674,717, discloses a process for preparing flame-retardant polyurethane foams by admixing starch with phosphoric acid at an elevated temperature and oxyethylating the resulting mixture to yield a starch-phosphorus-based polyether useful as a reactant in the preparation of urethane foams with flame-retardant properties.
Another method of producing flame retardant polyurethane foams, as disclosed in U.S. Pat. No. 3,658,731 is by reacting either dry whey containing lactose or torula yeast protein with a polyisocyanate in the presence of dimethyl sulfoxide. U.S. Pat. No. 3,629,162 discloses a similar process. Both patents emphasize the important role of the protein in the whey or yeast as a participant in the reaction.
British patent specification No. 1,440,831 claims the production of isocyanurate foams by reactions of isocyanates with tri-, tetra- or higher polysaccharides. The examples however, all require the presence of conventional polyols. Moreover, the reactions require the presence of isocyanurate ring producing catalysts as opposed to polyurethane producing catalysts.
An article in Journal of Cellular Plastics, August, 1967 by Bennett et al describes the preparation of polyurethane foams by reaction of a specific polyol, N,N,N.sup.1,N.sup.1 -tetrakis(2-hydroxypropyl)ethylene diamine with a polyisocyanate in non-aqueous media in the presence of starch containing not more than 10% moisture. Other products were similarly prepared by replacing the starch with dextrin.
Yet another method for preparing flame-retardant polyurethane foams is disclosed in Applicant's U.S. Pat. No. 4,291,129, wherein the foam composition is based on a polyurethane made from a polyisocyanate, a conventional industrial polyol, an aqueous slurry or solution of untreated carbohydrate, calcium acid phosphate, sodium aluminum sulfate, and sodium bicarbonate. The reactive mixture may contain one or more flame retardants to produce flame resistant foams.